MATEC Web of Conferences 13 , 06004 (2014)
DOI: 10.1051/matecconf/ 201 4 13 06004
C Owned by the authors, published by EDP Sciences, 2014
Potentials of Selected Malaysian Biomasses as CoGasification Fuels with Oil Palm Fronds in a Fixed-Bed
Downdraft Gasifier
Mohamad Nazmi Zaidi Moni1,a, Shaharin Anwar Sulaiman2 and Suhaimi Hassan3
1, 2, 3
Mechanical Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar,
31750 Tronoh, Perak, Malaysia.
Abstract: Oil palm frond (OPF) has been successfully gasified to produce syngas and
has since deemed as a potential source of biomass fuel in Malaysia. However, if OPF is to
be utilized as a main fuel for industrial-scale firing/gasification plant, interruption in fuel
supply may occur due to numerous reasons, for instance inefficient fuel processing and
ineffective transportation. A secondary supporting solid fuel is therefore necessary as a
partial component to the main fuel in such cases, where the secondary fuel is combusted
with the main fuel to adhere to main fuel shortage. Gasification of two fuels together,
known as co-gasification, is practiced worldwide, some in industrial scale. However,
current practice utilizes biomass fuel as the secondary fuel to coal in co-gasification. This
investigation explores into the feasibility of co-gasifying two biomass fuels together to
produce syngas. OPF was chosen as the primary fuel and a selection of Malaysian
biomasses were studied to discover their compatibility with OPF in co-gasification.
Biomass selection was made using score-and-rank method and their selection criteria are
concisely discussed.
1 Introduction
From previous work, it was observed that biomass gasification of oil palm fronds (OPFs) has a
good potential as biomass fuel to produce syngas [1&2]. Besides, a preliminary analysis on the
feasibility of OPF as well as the properties of the syngas from the gasification process was analyzed
[3&4]. In this work, the concept of a co-gasification reactor (oil palm waste and other biomass) is
introduced to avoid dependencies on either fuel source and to increase the total amount of power
generation. In order to ensure an uninterruptable operation in power plant from OPF fuel shortage, a
secondary fuel component may need to be combined with OPF to reduce the dependency on OPF
alone in a process known as co-gasification. The secondary fuel component may be processed from
other biomasses that are also available in large quantities or, in small quantities but not negligible, in
which they appear too little for any means of industrial utilization but co-gasification may be a golden
opportunity. While many co-gasification tests have been carried out using biomass-coal mix, the
proposed biomass-biomass mix has yet to be investigated, ergo, signifying the novelty in this
proposed study. In comparison with related works in biomass co-gasification, no known work
a
Corresponding author: nazmizaidi@yahoo.com
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Article available at http://www.matec-conferences.org or http://dx.doi.org/10.1051/matecconf/20141306004
MATEC Web of Conferences
involving OPF has been carried out, therefore adding another challenge in this study. From the
engineering research perspective this scenario needs to be explored and developed. This work
proposes to extend the idea of single fuel gasification reactor to a dual fuel system whereby the reactor
can operate with a flexible proportion of combined fuel in the event one of fuel sources experiences a
shortage or in abundance. The general objectives of this research are to identify and to conduct
investigations on biomasses that are feasible to be co-gasified with OPF in a downdraft gasifier to
produced synthesis gas. A score-and-rank method was used to assign a grade to each identified
biomass in terms of potentials as a co-gasification fuel.
2 Potential biomasses for co-gasification with OPF
2.1 Biomass Selection Characteristics
Biomasses were selected based on certain characteristics: morphology, C/H ratio, calorific value,
moisture content, supply and accessibility, and process requirements based on the specification of a
30 kW downdraft gasifier at Universiti Teknologi PETRONAS. The gasifier is known to have worked
efficiently with biomass fuels with the following characteristics:
x Morphology: high density, woody to fibrous biomass fuel with minimum crisscross dimension of
25 mm;
x C/H ratio: elemental C/H ratio within the range of that of general biomass, around 10
x Calorific value (CV): biomass fuel with high CV is more preferable to generate syngas of high
CV;
x Moisture content (MC): reduced to 30% and lower, best at equilibrium moisture content of 1015%;
x Supply and accessibility: biomass with production amount and easy accessibility is preferable to
ensure steady supply of fuel to gasifier and seasonal biomass is less preferable;
x Processing requirement: biomass that requires less processing (drying, size reduction, densification
etc.) has the higher advantage as a potential solid fuel due to less time and cost invested in
processing
Generally, biomass with low moisture content (30% and lower), moderate particle size (an acceptable
size of 10 to 50 mm in dimension), high bulk density (for higher energy density) and able to resist
decomposition has the advantage as a potential source of solid fuel with respect to gasification.
3 Results and Discussions
3.1 Biomass Characteristics
The oil palm trunk (OPT), empty fruit bunch (EFB), palm mesocarp fiber (PMF) and palm kernel
shell (PKS) were reviewed for their potentials and compatibility for co-gasification with OPF. The
chemical compositions, calorific values, and proximate analyses, CV and produced amount of the
chosen biomass are shown in Table 1. All biomasses were found to have a carbon content range of 38
– 50 wt. % and a hydrogen content range of above 5 wt. %. PKS was found to have the highest carbon
content at 49.65 wt. % while paddy straw the lowest at 33.48 wt. %. Sawdust has the highest hydrogen
content at 6.50 wt. % and OPT has the lowest at 5.09 wt. %. The carbon contents of the selected
biomasses were found to be within that of super-compliance sub-bituminous and lignite coal (in
between 35 – 50 wt. %) at as-received condition [5]. The hydrogen contents of the selected biomasses
were also found to be comparable to that of the same types of coal at 2 – 4 wt. % at as-received
condition. The nitrogen and sulfur contents of the selected biomasses were discovered to be
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comparable to low-rank coal as well. With the exception of OPT, paddy straw and EFB, all biomasses
have nitrogen content of lower than 1.0 wt. %. The higher amount of nitrogen in OPT, paddy straw
and EFB was fairly due to the usage of nitrogen-rich fertilizers in oil palm and rice plantation that is
localized for plant growth and crop production. Except for PMF, all biomasses have sulfur content of
lower than 0.5 wt. %. The relatively low contents of nitrogen and sulfur in the selected biomasses
compared to coal may contribute to low emissions of the corrosive oxides of sulfur and nitrogen
(NOx, SOx) from their combustion and thus require a less yield gas cleaning system, thus making the
biomasses favorable as fuels for general combustion application. The CV range of the selected
biomasses was found to be in between 13.8 – 20.5 MJ/kg which is within the range of that of supercompliance coal and lignite coal of in between 15 – 20 MJ/kg at as received condition. PKS and
sawdust, being the only hardwood-like biomasses in the selection, have the highest CV at 20.40 MJ/kg
and 20.45 MJ/kg respectively while fibrous paddy straw has the lowest CV at 13.74 MJ/kg. Overall,
all biomasses but paddy straw, rice husk and bagasse were found to have higher CVs than that of OPF
and are favorable for co-gasification with OPF, with respect to energy content considerations.
Table 1: Elemental components and calorific values (CV) of Malaysian biomasses [6-8]
Proximate analysis, wt. %
Elemental Components, wt. %
Amount,
Mton/year
FC
VC
MC
Ash
C
H
N
S
O
CV,
MJ/kg
Rice Husk
18.03
50.97
13.08
0.44
38.74
5.83
0.55
0.06
93.56
14.97
0.44
Paddy
Straw
9.22
59.97
8.47
0.78
33.48
6.01
1.46
0.15
92.38
13.74
0.78
Bagasse
15.91
80.19
52.20
0.12
42.93
5.82
0.68
0.06
93.44
15.25
0.12
EFB
9.89
84.61
66.26
2.61
40.73
5.75
1.4
0.22
51.9
18.6
2.61
PMF
11.38
81.52
45.23 18.74 40.97
5.93
0.77
0.51
51.82
18.66
18.74
OPF
12.91
83.19
71.43
6.31
42.1
5.46
0.7
0.13
51.91
15.59
6.31
OPT
11.42
76.84
75.90
4.19
40.64
5.09
2.15
0
53.12
17.27
4.19
PKS
14.87
81.03
17.50
6.41
49.65
6.13
0.41
0.48
43.33
20.4
6.41
Sawdust
16.20
78.80
16.30
>1.0
47.2
6.5
0
0
46.3
20.45
>1.0
Type
Note: FC: fixed carbon; VM: volatile matter; MC: moisture content; CV: calorific value
Fixed carbon is the amount of solid carbon left after a solid fuel undergoes full devolatilization and
acts as the main heat generator during combustion [9]. Commonly, biomass fuels have a fixed carbon
content range of 10 – 30 wt. % [10]. The proximate analyses of the selected biomasses showed that all
but paddy straw and EFB have fixed carbon contents of above 10 wt. % with rice husk being the
highest at 18.03 wt. %. High volatile contents were observed where all biomasses have more than 70
wt. % of volatiles except for rice husk (50.97 wt. %) and paddy straw (59.97 wt. %), which are still
not so far off from average. Volatile matter refers to the components of carbonaceous fuel (except
moisture) that are liberated in gaseous form at high temperature in the absence of air, mostly heavy
hydrocarbons and aromatics, that are important elements for further thermochemical processes to form
syngas. Amount of volatile matter proportionately helps in easier ignition of fuel [9]. High volatile
contents were observed where all biomasses have more than 80 wt. % of volatiles except for OPF
(76.84 wt. %) and sawdust (78.8 wt. %), which are still not so far off. The volatile contents of the
selected biomasses were also found to be higher than that of coal which commonly is in the range of
30 – 40 wt. %.
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For combustion purposes, only 30% and below moisture content in fuel is deemed acceptable. All
biomasses have as-received moisture content of more than 30% except for PKS, paddy straw, rice
husk and sawdust, mostly due to their small particle size that makes drying easier and their hardwood
properties that stores less moisture than fibrous structure does. This means that all biomasses with
more than 30% as-received moisture content need to undergo drying process to keep their optimal
properties and to maintain their quality as solid fuel prior to being utilized for combustion. The ash
contents for all biomasses were below 10 wt. % except for rice husk and paddy straw that were the
highest at 22.0 wt. % and 18.3 wt. % respectively, and generally were comparable to that of coal. Low
ash content signifies lower risks of slagging due to accumulation of molten ash from exposures to high
temperature during combustion and consequently lower risks of reactor operation problems [10]. Also,
low ash content implies a lesser space and handling needed to manage ash storage and removal.
3.2 Supply and Availability
Other than OPT, OPF and paddy straw, all the biomasses are available as processed biomass byproducts at respective processing mills. Residue biomasses such as OPT, OPF and paddy straw are
available at their respective plantation origin, mostly from harvesting and felling. Most paddy and oil
palm plantations in Malaysia are easily accessible using land vehicle and this eases the transportation
of biomass out from the plantations using bulk carrier vehicles, although some plantations may not be
spared with modern road access. As for mill refuse biomasses, they can be collected in-situ,
commonly in crushed and ground forms. Most processing mills are located near to modern road and
facilities, and are easy to access. In terms of availability, OPF tops the list with more than
18.7 Mton/year supply, followed with EFB, PMF, PKS and OPT, in that order, for oil palm-derived
biomasses. Sawdust was estimated to be produced at more than 1 Mton/year while rice husk, paddy
straw and bagasse were produced at less than 1 Mton/year. Rice husk, paddy straw, bagasse and OPT
are produced seasonally, therefore their amounts only peak at harvesting and felling (for OPT) period,
and is a disadvantage in creating a continuous biomass fuel supply throughout the year from these
sources. However, with proper processing and storage, they could withstand a longer storing time for
out-of-season utilization.
3.3 Potential Biomass Score and Rank
Score and rank method was used to select the biomass fuel sources using their potentials based on the
discussed selection criteria. A simple ranking method was used to sort the biomasses from the most to
less favorable as biomass fuel for co-gasification with OPF using their attributes. Eight main attributes
were used for the ranking process: volatile content, moisture content, calorific value, annual
production, supply availability, drying requirement and briquetting/densification requirement.
Biomasses with high volatile content, high calorific value, large amount of annual production, highly
available, low moisture (therefore low requirement for drying) and large particle size (eliminates the
need for briquetting/densification) are highly favorable as co-gasification fuel with OPF. The results
of the ranking process are shown in Table 2. From the results it was discovered that herbaceous
biomass such as bagasse, rice husk and paddy straw scored the lowest compared to fibrous and woodlike biomass. PKS tops the list for it fulfilled all the preferred criteria as biomass fuel, followed with
PMF, sawdust, EFB and OPT.
4 Conclusion
Potential biomasses for fuel production to be used in co-gasification with OPF were reviewed and
ranked. It was found that most Malaysian biomasses are eligible to be used as fuel, provided that they
undergo certain processing methods in order to become solid fuels that are optimized for downdraft
co-gasification process. With this preliminary data, further detailed analyses can be carried out to
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study the fuel compatibility in gasification and their gasification yields. Overall, the objectives of the
preliminary study were met and the results were positively viewed as a constructive progress in this
particular research.
Table 2: Ranking of selected biomass based on selection criteria
Type
VM
MC
CV
C/H
AP
SA
DR
BD
Score
Rank
PKS
6
6
8
9
6
1
0
0
36
1
PMF
7
5
7
3
8
1
1
0
32
2
OPF
8
2
4
7
9
1
1
0
32
–
Sawdust
4
7
9
5
4
1
0
1
31
3
EFB
9
3
6
4
7
1
1
0
31
4
OPT
3
1
5
8
5
0
1
0
23
5
Bagasse
5
4
3
6
1
0
1
0
20
6
Rice Husk
1
8
2
2
2
0
0
1
16
7
Paddy Straw
2
9
1
1
3
0
0
0
16
8
Note: VM: volatile content (highest=9, lowest=1); MC: moisture content (highest=1, lowest=9); CV, calorific
value (highest=9, lowest=1); C/H, carbon-hydrogen ratio (highest=9, lowest=1); AP, annual production
(highest=9, lowest=1); SA, supply availability (all time=1, seasonal=0); DR, drying requirement (yes=0, no=1);
BD, briquetting/densification requirement (yes=0, no=1);
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